Thanks - this was the critical context:
G2: 10 tanks in Romania
G3: 6 tanks in Romania pay off $20 in damage
G4: start building tanks in Berlin to avoid paying $20 to repair factoryTraded border areas a couple times and then full on retreat to Moscow began leaving single inf to slow Germany down
On G5 Germany has massive stack of tanks and mechs and some infantry with a lot of bombers a couple spaces back with smaller army from Bryansk.
The value of infantry in lieu of bombers, wins out. Changing a battle calc from 30inf, 2 art, 2 tank, 2 fight, 1 tac, 8 bombers to 60 inf, 0 bomber, all else equal, boosts the %win from mid 65 to 97 when going against 5 inf, 15 mech, 20 tanks, no AAA (1st scenario drops to 37% with 2 AAA defending. I think this is why all the pushback. I agree, against a stalled out German attack (the trading border territories you mentioned) the bombers would indeed help manage dead zones for max German inf loss, preserving Soviet territory. However, advanced German players will rarely, if ever, have a stalled out attack, and will not be trading territories on the border for multiple rounds.